Light output from a light source is focused on a surface or an inside of an object, so that processing or the like can be performed in a focusing region of the object. As one of focusing technologies, technology called simultaneous spatial and temporal focusing (hereinafter, referred to as “SSTF”) is known (refer to Non Patent Documents 1 and 2).
SSTF is as follows. Pulsed light (for example, ultra-short pulsed laser light) having a certain wavelength band is dispersed by a dispersive element, and light is output to an optical path different according to a wavelength. Further, light of each wavelength output from the dispersive element is focused by a focusing element on a common region via the optical path different according to the wavelength. As an example of the dispersive element, a diffraction grating pair or a prism pair is used. A direction or a position of each diffraction grating or each prism is adjusted, so that timing of light of each wavelength arriving at the focusing region can be set.
In SSTF, the light of each wavelength dispersed by the dispersive element and arriving at the focusing region by the focusing element passes through the optical path different according to the wavelength, and further, arrives at the focusing region at timing different according to the wavelength. Therefore, a light energy density increases in the focusing region, and on the other hand, the light energy density decreases in an optical path until reaching the focusing region, so that an influence on the object is reduced. Further, a temporal waveform of pulsed light in the focusing region can be adjusted.